Webs, films, and laminates made from low density, high comonomer content elastomeric fibers and films are used for a variety of applications where stretchability is required. For instance, waist bands, leg bands, feminine care products, adult care products, and diapers employ elastic components in order to supply such articles with elastic properties and a better fit.
Various methods for producing such elastic products have been previously disclosed in the past. For instance, in U.S. Pat. No. 4,663,220 to Wisneski et al., which is incorporated herein by reference in its entirety, the synthesis of elastomeric products from polyolefin-containing extrudable materials is disclosed. In this reference, extrudable elastomeric compositions are formed by blending an A-B-A' block copolymer (where "A" and "A'" are each a thermoplastic endblock including styrene and where "B" is an elastomeric midblock) with a polyolefin. The above polymer blend is extrudable when subjected to elevated pressure and temperature conditions. The A-B-A' block copolymer imparts elastic properties to products formed from the composition.
Such compositions are extruded by being molded at an appropriate combination of elevated pressure and temperature. The pressure and temperature will vary depending on the polyolefin utilized. These extrudable compositions may be formed into a variety of products such as fibrous nonwoven elastomeric webs with varying basis weights. Herein, the terms "elastic" and "elastomeric" are used to refer to materials that, upon application of a force, are stretchable to a stretched length of about 125 percent of their original relaxed length.
However, when such elastomeric materials are released from a stretched position, the fibers typically do not return to their original relaxed length, but exhibit permanent elongation. For example, if an elastic laminate is stretched over a surface and left in this stretched or stressed situation for a period of time, the resistive forces that the elastomeric fibers in the laminate exert on the surface diminish. Thus, when the laminate is removed from the surface and released from its stretched position, the fibers within the laminate will have become permanently elongated when relaxed, reducing the stretch characteristics of the fabric. This elongation process is known as stress relaxation.
When such stress relaxation occurs within elastomeric fibers, the performance of such fibers is negatively affected. Fibers that have undergone significant stress relaxation will not supply laminates with needed fit properties and holding power.
Thus, a need currently exists for a process to improve the performance of elastomeric fibers so that they will undergo significantly less stress relaxation.